When humans disappear, biodiversity takes a surprising turn

Less than an hour’s train ride from central Tokyo, ecologist Kei Uchida walks through glades of mountain cherry trees and meadows filled with susuki grass as tall as an elephant. The researcher smiles when he spots something by the trail: a tangled orb of grass stalks, at about knee height. It is the nest of the tiny Eurasian harvest mouse (Micromys minutus), a species that has been on the decline in this area and has been targeted for protection.

Volunteers saved this location around Mount Tenran from development 30 years ago, and today they monitor its plants and animals, thin its forests and even plant and harvest rice — all in the name of biodiversity. Here, nature needs people. In the shallow water of the rice paddy, fish as small and arched as an eyebrow swim, and just above the water’s surface, dragonflies mate. At dusk, fireflies dance above the fields.

Uchida, an environmental scientist at Tokyo City University in Yokohama, and his colleagues included this site in a study of thousands of species in more than 150 wooded, agricultural and ‘peri-urban’ landscapes in Japan1. Unsurprisingly, they found that the diversity and abundance of most species declined at sites where the human population was growing. But they also found that biodiversity declined in places where the number of people was decreasing (see ‘Lost life’). This result — and others like it in different parts of the world — contradicts the common assumption that when people leave, nature always thrives.